1. Field of the Invention
The invention relates to a fuel injection nozzle having a nozzle body, which body has one first and one second group of injection ports, one first and one second nozzle needle, and one separate pressure chamber for each nozzle needle, so that the nozzle needles are adjustable independently of one another between a closed position, in which the injection ports associated with the corresponding nozzle needle are closed, and an injection position, in which the corresponding injection ports are opened. The invention also relates to a method for operating a fuel injection nozzle.
2. Description of the Prior Art
From German Patent Disclosure DE 40 23 223 A1, a fuel injection nozzle of this type is known. The injection ports of one group are each disposed along a circle, forming an inner circle and an outer circle concentric with it. The nozzle needle associated with the outer injection ports is embodied as a hollow cylinder, and the nozzle needle associated with the inner injection ports is disposed in the interior of the hollow nozzle needle. Between the inner nozzle needle and the outer nozzle needle is a separating sleeve, which is urged by a compression spring into contact with a sealing seat in the nozzle body, that is embodied between the two circles of injection ports. The inner injection ports are used for the pre-injection, while the outer injection ports are provided for the main injection. In each case, the separating sleeve assures that the two groups of injection ports remain separated from one another during the opening of the nozzle needles.
The comparatively high engineering expense is a disadvantage of this known construction. Since the injection ports of the two groups are located quite close together, both the two nozzle needles and the separation sleeve have to be accommodated in a very small space.
The object of the invention is to refine an injection nozzle of the type defined at the outset in such a way that a simpler design is achieved. Furthermore, flexible use of the two groups of injection ports is to be enabled by means of suitable triggering of the two nozzle needles. The object of the invention is also to create a method for operating an injection nozzle of the type defined at the outset.
The fuel injection nozzle of the invention has the advantage that the separation sleeve or a similar sealing element between the two nozzle needles can be dispensed with. This design is based on the recognition that sealing off of the applicable injection ports of one group, even when the nozzle needle is open, can be reliably attained for the injection ports of the other group without requiring a separate seal.
In a preferred embodiment of the invention, for at least one of the nozzle needles, a stop chamber is provided, which is provided with a hydraulic connection. In this way, a hydraulic stroke stop for the applicable nozzle needle is created that limits the opening motion of the nozzle needle more gently than a typical mechanical stroke stop. A longer service life of the nozzle needle is thus attained.
The method according to the invention offers the advantage that arbitrarily, the various injection ports can be used for the pre-injection and the main injection. In this way a vario effect can be attained, since by the suitable triggering of one of the two nozzle needles or both nozzle needles, the total cross-sectional area of the injection ports can be adapted to the particular injection. If for a relatively long time only one row of ports is activated, then by suitable, under some circumstances only brief, switchover to the other row of ports, carbonization of the first row of ports can be prevented. The method can in principle also be used in an injection nozzle in which between the two nozzle needles a separation sleeve is provided, which facilitates the sealing between the various rows of ports.